The incidence of nephrolithiasis in the USA rose by more than 60% over the last 3 decades, and there is considerable morbidity associated with kidney stones; therefore, there is a critical need to determine the underlying mechanism(s) involved in stone formation. The overall objective of this application is to develop an in vitro model system to study the two stages of idiopathic nephrolithiasis: 1) the deposition of calcium phosphate (CaP) in the form of Randall's plaque (RP), and 2) the subsequent overgrowth of RP with calcium oxalate (CaOx), forming a composite stone. The central hypothesis of this proposal is that the acidic proteins present in urine and renal tissues may induce a non-classical crystallization process, called the polymer- induced liquid-precursor (PILP) process, and that this process may be responsible for many of the structural features found in stones. The rationale for developing an in vitro model system is that it can be used to sort out and test species isolated from urine and renal tissue to see how they separately, or in combination, influence the 'biomimetic stone' formation. Such a model system can then be used to help identify protocols and/or therapeutic agents for treatment or prevention of the disease. Specific Aim 1 will determine if a biomimetic RP model system of stage I can be developed. Artificial basement membrane and interstitial tissue will be mineralized by the PILP process to determine if nanostructural features relevant to RP, such as multi- laminated spherules and collagen mineralization, can be duplicated in vitro. Specific Aim 2 will determine if a biomimetic stone model system of stage II can be developed, where the plaque developed in Aim 1 will serve as a nidus for overgrowth of CaOx. Specific Aim 3 will determine the influence of urinary conditions on the in vivo overgrowth of CaOx on the biomimetic plaque placed in a rat urinary bladder, and will analyze structural features of the resulting stone for comparison to the biomimetic 'stones' i Aim 2, and to native stones. In Aims 2 and 3, native plaque from human renal tissues will be tested for comparison. The combination of all three aims will enable the development of mineralogical 'signatures', which can then be deciphered to clearly point to the influence of various species on the formation mechanism of a stone. The proposed research is innovative because it provides an entirely different perspective on the role of macromolecules in stone formation, where it is hypothesized that osteopontin is a key player in a PILP type process. In addition, for the first time, an in vitro model system can be developed that encompasses both Stage I (plaque formation) and Stage II (stone formation) of idiopathic nephrolithiasis. This in turn provides the tools needed to test the influence of various species on the formation of stones, with information provided at multiple stages of the process. The significance of this work is that it will enable the development of biomarkers for evaluation of stone formation mechanism(s); development of treatment protocols and/or therapeutic agents; and a mechanistic understanding which can lead to preventive measures against the occurrence and recurrence of stones.